Polycarbonates are well-known commercially available resinous materials having a variety of applications. They are typically prepared by the reaction of dihydroxy compounds with a carbonate precursor, such as phosgene, in the presence of a catalyst. Methods of direct phosgenation, interfacial condensation and transesterification, for the preparation of polycarbonates, are described in detail in "The Chemistry and Physics of Polycarbonates", by H. Schnell, John Wiley & Co., N.Y., 1964.
Polycarbonates are high temperature, high performance engineering thermoplastics having a combination of good thermal and mechanical properties, especially when prepared from one or more aromatic diols. The blending with polycarbonates of additional compounds, such as for example, other thermoplastic resins, copolymer rubber compounds, and the like, is commonly practiced in order to improve one or more properties of the homopolymer polycarbonate.
The applications for homopolycarbonates and blends of polycarbonates with other thermoplastic resinous compounds as engineering materials are limited because they generally exhibit severe environmental stress failure. By environmental stress failure is meant surface crazing or cracking, or disintegration of the molded piece resulting from its contact with organic solvents while under stress, such as may occur for example when solvents are used to clean or degrease stressed parts fabricated from polycarbonates or polycarbonate blends.
U.S. Patent No. 3,431,224 discloses a blend of a polycarbonate and a polyolefin such as polyethylene or an olefin copolymer such as ethylene/propylene, in order to improve the environmental stress failure resistance of the homopolycarbonate. U.S. Patent No. 4,180,494 discloses the use of a butadiene-based core-shell copolymer for improving the environmental stress failure resistance of a blend of polycarbonate and polyester resins.
Various other additives are disclosed in the art for modifying the properties of polycarbonate/polyester blends; U.S. Patent No. 4,476,274 discloses polyethylene and glass fibers for improved impact resistance; U.S. Patents Nos. 3,780,139 and 4,271,063 disclose a terpolymer of ethylene, carbon monoxide and a third component such as vinyl acetate for improved strength; U.S. Patent No. 4,639,481 discloses polyethylene or a polyolefin copolymer for improved impact resistance.